This invention relates to the measurement of electrical conductivity. More specifically, the invention relates to the measurement of the electrical conductivity of fluid solutions.
Prior art instrumentation for measuring the conductivity of solutions generally utilize an AC signal applied to a conductivity cell containing a pair of electrodes which are immersed in the test solution. The more accurate commercial instruments use an AC bridge design with the cell as one arm of the bridge and manual balancing to a null point. Instruments of this type are typified by U.S. Pat. No. 3,086,169.
Alternatively, other techniques have been used in the prior art which may be classified as steady state DC techniques. In the steady state DC techniques the potential drop between a pair of electrodes supplied with a steady state constant current from a constant current DC source is measured. In such systems the current required to provide a predetermined potential drop between a pair of measurement electrodes then provides a measurement of the conductivity of the solution in a test cell between the electrodes. Systems of this type are typified by U.S. Pat. No. 3,646,436.
All of these prior art techniques have difficulty with electrolysis of the test solution together will effects due to polarization of the test solution. The term polarization will be used here to designate all electrochemical voltage differences other than that due to the passage of the test current through the solution.
The present invention avoids many of the difficulties encountered in the use of prior art systems and in so doing provides a simple and economical means for measuring the conductivity of test solutions.